#include <bits/stdc++.h>
using namespace std;
int main(){
	int x;
	float t;
	cin>>x;
	t=(x*0.9+x*0.8+x)/3;
	printf("%.1f",t);
    }
/**************************************************************
	Problem: 1613
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/